Stim1 Binds to Pairs of Orai1 Subunits to Open the Crac Channel

Yen, Michelle; Lokteva, Ludmila A.; Lewis, Richard S.

doi:10.1016/j.bpj.2013.11.1820

Cited by 3 publications

(7 citation statements)

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“…1 that reveal Orai1 clustering mediated by the SOAR dimer. The increased channel function provides further evidence that the SOAR dimer preferentially interacts through unimolecular interactions with two different hexameric Orai1 channels as opposed to a bimolecular interaction with two adjacent Orai1 subunits within a single hexamer, as previously proposed (19)(20)(21)(22). Our studies continued to examine how cross-linking between channels may be controlled naturally, and what significance it may have in Ca 2+ signal generation.…”

Section: Yfp-s H -S H Yfp-s-s H Yfp-s H -S Hek Orai1-his Cells + Yfp-supporting

confidence: 66%

“…The compact, highly conserved SOAR units from STIM proteins, self-assemble into dimers that undergo coupling and activation of Orai1 channels, closely recapitulating the function of full-length STIM proteins (8-10, 17, 23). Our recent evidence (7, 17, 40) militates strongly against an earlier bimolecular coupling model for the STIM-Orai interaction (19)(20)(21)(22). Instead, we reveal that while SOAR must be presented to Orai1 as a dimer, the SOAR monomer units within the SOAR dimer interact independently in a unimolecular mode with single Orai1 subunits (17).…”

Section: Stim21 Modulates Ca 2+ Oscillations Through Impaired Orai1 supporting

confidence: 50%

“…Until now, it has been assumed that the localization of STIM1 within ER-PM junctions results in passive "herding" of Orai1 channels within these junctions. Indeed, the theory that STIM1 undergoes a bimolecular interaction with two adjacent Orai1 subunits in a single Orai1 hexameric channel (19)(20)(21)(22), precluded consideration of STIM-induced Orai1 channel cross-linking. Moreover, we reveal that bulky fluorescent tags on Orai1 sterically block Orai1 cross-linking, explaining why crosslinking was not previously recognized.…”

Section: Stim21 Modulates Ca 2+ Oscillations Through Impaired Orai1 mentioning

confidence: 99%

“…The SOAR1 dimer likely remains intact during the store depletion-induced unfolding of STIM1 and the subsequent association of SOAR1 with the Orai1 channel (15,17,18). It had been suggested that Orai1 channel activation occurs following a "bimolecular" interaction of the SOAR1 dimer in STIM1 with a pair of adjacent Orai1 subunits within the hexameric Orai1 channel (19)(20)(21)(22). We recently revealed that the exposed F394 residue in SOAR1 plays a pivotal role in both binding to and gating of the Orai1 channel (23).…”

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confidence: 99%

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Cross-linking of Orai1 channels by STIM proteins

Zhou

Nwokonko

Cai

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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The transmembrane docking of endoplasmic reticulum (ER) Ca-sensing STIM proteins with plasma membrane (PM) Orai Ca channels is a critical but poorly understood step in Ca signal generation. STIM1 protein dimers unfold to expose a discrete STIM-Orai activating region (SOAR1) that tethers and activates Orai1 channels within discrete ER-PM junctions. We reveal that each monomer within the SOAR dimer interacts independently with single Orai1 subunits to mediate cross-linking between Orai1 channels. Superresolution imaging and mobility measured by fluorescence recovery after photobleaching reveal that SOAR dimer cross-linking leads to substantial Orai1 channel clustering, resulting in increased efficacy and cooperativity of Orai1 channel function. A concatenated SOAR1 heterodimer containing one monomer point mutated at its critical Orai1 binding residue (F394H), although fully activating Orai channels, is completely defective in cross-linking Orai1 channels. Importantly, the naturally occurring STIM2 variant, STIM2.1, has an eight-amino acid insert in its SOAR unit that renders it functionally identical to the F394H mutant in SOAR1. Contrary to earlier predictions, the SOAR1-SOAR2.1 heterodimer fully activates Orai1 channels but prevents cross-linking and clustering of channels. Interestingly, combined expression of full-length STIM1 with STIM2.1 in a 5:1 ratio causes suppression of sustained agonist-induced Ca oscillations and protects cells from Ca overload, resulting from high agonist-induced Ca release. Thus, STIM2.1 exerts a powerful regulatory effect on signal generation likely through preventing Orai1 channel cross-linking. Overall, STIM-mediated cross-linking of Orai1 channels is a hitherto unrecognized functional paradigm that likely provides an organizational microenvironment within ER-PM junctions with important functional impact on Ca signal generation.

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Section: Yfp-s H -S H Yfp-s-s H Yfp-s H -S Hek Orai1-his Cells + Yfp-supporting

confidence: 66%

Section: Stim21 Modulates Ca 2+ Oscillations Through Impaired Orai1 supporting

confidence: 50%

Section: Stim21 Modulates Ca 2+ Oscillations Through Impaired Orai1 mentioning

confidence: 99%

mentioning

confidence: 99%

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Cross-linking of Orai1 channels by STIM proteins

Zhou

Nwokonko

Cai

et al. 2018

Proc. Natl. Acad. Sci. U.S.A.

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“…The authors interpreted this to imply that Orai channels may natively exist as tetramers, forming CRAC channels with high selectivity for Ca 2þ . However, another very recent study (69) utilized hexameric concatemers of Orai1 and introduced mutations to prevent STIM1 binding into individual subunits, concluding that Orai1 hexamers recapitulate the Ca 2þ -selectivity of native CRAC current.…”

Section: Orai Subunit Stoichiometrymentioning

confidence: 99%

Molecular Biophysics of Orai Store-Operated Ca2+ Channels

Amcheslavsky

Wood

Yeromin

et al. 2015

Biophysical Journal

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Upon endoplasmic reticulum Ca 2þ store depletion, Orai channels in the plasma membrane are activated directly by endoplasmic reticulum-resident STIM proteins to generate the Ca 2þ -selective, Ca 2þ release-activated Ca 2þ (CRAC) current. After the molecular identification of Orai, a plethora of functional and biochemical studies sought to compare Orai homologs, determine their stoichiometry, identify structural domains responsible for the biophysical fingerprint of the CRAC current, identify the physiological functions, and investigate Orai homologs as potential therapeutic targets. Subsequently, the solved crystal structure of Drosophila Orai (dOrai) substantiated many findings from structure-function studies, but also revealed an unexpected hexameric structure. In this review, we explore Orai channels as elucidated by functional and biochemical studies, analyze the dOrai crystal structure and its implications for Orai channel function, and present newly available information from molecular dynamics simulations that shed light on Orai channel gating and permeation.

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Store-Operated Calcium Channels

Prakriya

Lewis

2015

Physiological Reviews

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971

1,214

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Store-operated calcium channels (SOCs) are a major pathway for calcium signaling in virtually all metozoan cells and serve a wide variety of functions ranging from gene expression, motility, and secretion to tissue and organ development and the immune response. SOCs are activated by the depletion of Ca(2+) from the endoplasmic reticulum (ER), triggered physiologically through stimulation of a diverse set of surface receptors. Over 15 years after the first characterization of SOCs through electrophysiology, the identification of the STIM proteins as ER Ca(2+) sensors and the Orai proteins as store-operated channels has enabled rapid progress in understanding the unique mechanism of store-operate calcium entry (SOCE). Depletion of Ca(2+) from the ER causes STIM to accumulate at ER-plasma membrane (PM) junctions where it traps and activates Orai channels diffusing in the closely apposed PM. Mutagenesis studies combined with recent structural insights about STIM and Orai proteins are now beginning to reveal the molecular underpinnings of these choreographic events. This review describes the major experimental advances underlying our current understanding of how ER Ca(2+) depletion is coupled to the activation of SOCs. Particular emphasis is placed on the molecular mechanisms of STIM and Orai activation, Orai channel properties, modulation of STIM and Orai function, pharmacological inhibitors of SOCE, and the functions of STIM and Orai in physiology and disease.

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Stim1 Binds to Pairs of Orai1 Subunits to Open the Crac Channel

Abstract: Ca 2þ release-activated Ca 2þ (CRAC) channels mediate Ca 2þ entry in response

Cited by 3 publications

References 0 publications

Cross-linking of Orai1 channels by STIM proteins

Cross-linking of Orai1 channels by STIM proteins

Molecular Biophysics of Orai Store-Operated Ca2+ Channels

Store-Operated Calcium Channels

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